Coaxial multiband antenna



United States Patent 3,139,620 COAXIAL MULTEBAND ANTENNA Kenneth L. Leidy and Henry D. Cribbage, Washington,

D.C., assignors to the United States of America as represented by the Secretary of the Navy Filed Dec. 23, 1959, Ser. No. 861,726 6 Claims. (Cl. 34373tl) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to a coaxial antenna and in particular to one that may be grounded at one end and provided with a whip antenna at the other end.

There are times when it is desired to'operate a communication system on more than one band of frequencies. The arrangements in the prior art, accomplishing this objective, require a separate antenna for each band and are therefore unsatisfactory where weight and drag on a moving vehicle are important considerations. Further when more than one antenna is used, a transmission line for each antenna may be necessary which is undesirable since additional weight and equipment will be required.

Accordingly, it is an object of the present invention to provide a single antenna that may be used in transmitting as many bands of frequencies as desired.

Another object is to provide a coaxial antenna employing a pair of stubs connected shorted end to shorted end to obtain improved isolation over a broad band of frequencies.

Other objects and advantages will becomemore fully apparent from the following description of the annexed drawing wherein:

FIG. 1 is an embodiment of the present invention.

FIG. 2 is a more detailed showing of the antenna feed arrangement in the embodiment of FIG. 1. V

In accordance with the teachings of the present invention, a coaxial antenna is provided by positioning a pair of stubs on a member, the first a predetermined distance on one side and the second a predetermined distance on the other side of the center of a radiating section. Each stub, which is a quarter wavelength long, includes a shorting Washer and at its lower edge is connected through the washer to the member and hence at its upper edge presents a high impedance to a first band of frequencies. The stubs are positioned on the member so that the section between the stubs functions as a dipole for transmission of a first band of frequencies. Another pair of tubular stubs are similarly positioned on either side of the center of another radiating section on the member to provide transmission on a second band of frequencies, and it is understood that the number of bands that may be transmitted in this manner is limited only by such considerations as the impedanceand size of the antenna.

In a center fed embodiment of the inventive concept, a pair of stubs connected shorted edge to shorted edge are located on each end of the antenna to provide a high impedance over a broad band of frequencies. A whip is positioned on one end and the other end of the antenna is grounded.

Referring to FIG. 1, sections 8, 9, which are part of member 10, are selected to be cylindrical although other shapes may be used. Section 8, positioned between stubs 11 and 12, functions as a dipole transmitting signals in a first band of frequencies. Stubs 11 and 12 each have an open end and a shorted end, the latter including washers 13 and 14, respectively. Each stub has a length sub stantially equal to one quarter the wavelength of the frequency approximately in the center of the first band, thereby offering a high impedance to the frequencies in that band. Similarly, section 9 is positioned between stubs 21 and 22 each having an open end and a shorted end. The latter include washers 23 and 24, respectively, and have a length substantially equal to one quarter the wavelength of the frequency approximately in the center of a secondhand. Thus, each stub 21, 22 offers a high impedance to the frequencies in the second band on which section 9 functions as a dipole. Stubs 11, 12, 21 and 22 are positioned longitudinal with member 10.

The diameters of sections 8, 9 and stubs 11, 12, 21, and 22 are selected to obtain an optimum standing wave ratio on each band with minimum weight and size.

Rods 25, which in this embodiment are selected to be eight in number, are positioned around Washer 24 and function as a stub since they have the same length as stub 22 and are shorted to member 10 at one end by Washer 24 and are connected together at the other end by washer 33. Similarly, rods 29, eight in number, are positioned around washer 23, are shorted to member 10 by washer 23 andconnected together by washer 30 and function as a stub having the same length as stub 21. Washers 30, 33 are insulated. from member 10. Finally, whip antenna 28, transmitting on a third band of frequencies, is positioned on washer 24 and theend of member 10 opposite the Whip antenna is grounded.

As shown in detail in FIG. 2, the antenna is centerfed at insulator 34 by the center conductor 31 of a coaxial transmission line. The outer conductor of the transmission line may be connected to member 10 at its base so that the portion of member 10 between insulator 34 and the base form the outer conductor of the transmission line and conductor 31 the inner conductor. If the transmission line formed by conductor 31 and member 10 does not exactly match the impedance of the dipolesS, the efiiciency of the antenna may be improved by inserting a conventional impedance transforming 1 section in series with inner conductor 31. Such a transforming section is shown in the drawing at 32 as a section of transmission 'line having a larger center conductor to provide a different characteristic impedance than that of conductor 31. The upper halves of dipoles 8 and 9'and the whip antenna 28 are ungrounded and are fed at as shown in FIG. 2 where transmission line inner conductor 31, or transforming section 32 as illustrated, passes through insulator 34.

The following table sets forth the dimensions of sections, stubs and rods that have been found satisfactory in the operation of the embodiment disclosed in FIG. 1. It should be understood that the table is exemplary only Whip 28 is made of stainless steel, while member 10 and stubs 11, 12, 21 and 22 may be either brass or stainless steel. All voids are filled with machined polystyrene to make a solid rigid cylinder.

In operating the embodiment disclosed, a frequency in one of the three bands, or with proper multicouplers, three frequencies, one in each band may be applied to line31. Since stubs 10, 11 offer a high impedance to frequencies in the first band, signals in this band are transmitted by section 8. Stubs 21, 22 and rods 25, 29, the latter functioning as inverted stubs, provide a high impedance to frequencies in the second hand which are transmitted by section 9, while the whip antenna 28 transmits signals in the third band. Sections 8 and 9 each operate as a dipole. Since stubs 11 and 12 are a quarter wavelength at the first band frequency and have their open ends directed toward insulator 34, member will appear to have only the length of section 8 to frequencies at the first band and therefore will see an efficient half wave resonant dipole antenna. Similarly, frequencies at the second hand will see a high impedance at the innermost ends of stubs 21 and 22 since they are open ended quarter wave stubs at the second band frequency. To assist the second band frequency not seeing the member 10 beyond section 9, another pair of stubs having their open ends facing the other way may be added so that any signal of the second band frequency venturing down member 10 in either direction beyond stubs 21 and 22 will again see a high impedance. Such additional stubs can be made identical to stubs 21 and 22 except for their reversed position, or as shown in FIG. 1, may be made from a series of quarter wavelength rods as shown at 25 and 29. If a sutficient number of rods are used they will be the electrical equivalent of a cylindrical stub but may be desired in certain applications because they will offer less resistance to wind and water. Whip antenna 28 is connected to the feed point at 80 through the portion of member 10 between washer 24 and insulator 34, and will operate as a non-resonant vertical mast antenna.

Obviously many modifications and variations of the ,present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A vertical collinear multiband antenna comprising;

a vertically oriented hollow mast and an insulator separating said mast into upper and lower collinear sections,

a coaxial antenna feed line disposed within said lower section and having its inner conductor connected to said upper mast section and its outer conductor connected to said lower mast section,

a first pair of cylindrical sleeves larger in diameter than said mast and coaxially mounted thereon on each side of said insulator, each sleeve having its end remote from the insulator electrically connected to said mast and having its unconnected end located an electrical distance from said insulator equal to the electrical length of the sleeve,

a second pair of cylindrical sleeves coaxially mounted on said mast adjacent the remote ends of said first pair of sleeves, each of said second pair of sleeves having its remote end connected to said mast and having its unconnected end located an electrical distance from said insulator equal to the electrical length of the sleeve.

2. An antenna as in claim 1 wherein the upper mast section extends beyond the upper sleeve of said second pair of sleeves a length several times the length of said sleeve.

3. An antenna as in claim 2 wherein said second pair of sleeves is larger in diameter than said first pair of sleeves.

4. An antenna as in claim 3 wherein the mast section defined by the unconnected ends of said first pair of sleeves is a pair of quarter wave dipoles at ultra high frequency, the mast section defined by the unconnected ends of said second pairs of sleeves is a pair of quarter wave dipoles at very high frequency, and the upper mast section is an efficient high frequency radiator.

5. An antenna as in claim 3 wherein each of the first pair of sleeves is a quarter wavelength at ultra high frequency, each of the second pair of sleeves is a quarter wavelength at very high frequency and the upper mast section is an efiicient radiator at high frequency.

6. An antenna as in claim 2 having a plurality of conducting parallel rods disposed at the remote ends of each of said second pair of sleeves, said rods being connected to said sleeves and insulated from said mast at their remote ends, said rods being of the same length as said second pair of sleeves.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,136 Hansell et a1. Apr. 5, 1938 2,486,597 Greene Nov. 1, 1949 2,535,298 Lattin Dec. 26, 1950 2,648,768 Woodward Aug. 11, 1953 FOREIGN PATENTS 1,013,728 Germany Aug. 14, 1957 

1. A VERTICAL COLLINEAR MULTIBAND ANTENNA COMPRISING; A VERTICALLY ORIENTED HOLLOW MAST AND AN INSULATOR SEPARATING SAID MAST INTO UPPER AND LOWER COLLINEAR SECTIONS, A COAXIAL ANTENNA FEED LINE DISPOSED WITHIN SAID LOWER SECTION AND HAVING ITS INNER CONDUCTOR CONNECTED TO SAID UPPER MAST SECTION AND ITS OUTER CONDUCTOR CONNECTED TO SAID LOWER MAST SECTION, 